64 • Technologies To Maintain Biological Diversity 



Figure 3-1.— Currently Described Species 



3% Vertebrates 2% Bacteria 



\and protozoa 

 / 

 invertebrates 



8% Noninsect 

 arthropods 



9% Algae, 

 fungi, and ferns 



14% Flowering 

 plants 



Of ttie currently described species, insects make up more 

 than half the total. The number of flowering plants described 

 are less than one-third of the percentage of insects. 



NOTE: Percentages rounded to nearest whole number. 

 SOURCE: Office of Tecfinology Assessment, 1986. 



lands were deforested 1,000 years ago (22). Ero- 

 sion from the deforested and overgrazed Arme- 

 nian hills, which eventually led to the demise 

 of productive agriculture in Mesopotamia, ap- 

 parently began over 2,000 years ago (21). These 

 kinds of changes undoubtedly caused local and 

 regional losses of diversity. 



What is new today is the scale on which re- 

 source degradation is occurring and thus the 

 rate at which diversity is apparently being re- 

 duced. Fishing, hunting, and gathering beyond 

 the capacity of ecosystems continues today, but 

 the effects are being greatly exacerbated by 

 degradation of ecosystems and significant re- 

 ductions in natural areas. The decline of fish- 

 eries and sharp reduction of diversity in the 



Chesapeake Bay over the past two decades is 

 an example well known to Congress, which has 

 supported several initiatives to improve under- 

 standing of the complex syndrome of overfish- 

 ing, pollution, and hydrologic changes related 

 to the region's development. 



Acceleration of resource degradation and 

 diversity loss is partly a consequence of popu- 

 lation growth, especially in rural areas of de- 

 veloping countries, where compound growth 

 rates are often more than 1 percent per year. 

 It is also a consequence of technologies devel- 

 oped over the past century that have enabled 

 humans to devastate natural ecosystems even 

 where population densities or growth rates are 

 moderate. For example, modern drainage tech- 

 niques and market conditions make accelerated 

 wetland drainage possible in the United States, 

 and veterinary drugs and modern well-drilling 

 machinery enable African farmers to build live- 

 stock herds above the natural carrying capac- 

 ity of their rangelands. 



Accelerated loss of diversity is also caused 

 by modern transportation, which reduces the 

 effect of geographic barriers important in the 

 evolution of diversity. Exotic species, diseases, 

 and pests were for centuries carried across 

 oceans, mountains, and deserts by hundreds 

 of people traveling in ships and on foot, but now 

 they are carried by hundreds of thousands of 

 people traveling in trucks and airplanes. 



Biologists and agriculturalists have thus be- 

 come alarmed about the scale of plant and ani- 

 mal resource degradation during the last two 

 to three decades. The alarm stems from obser- 

 vations of extensive reductions in habitat, cou- 

 pled with a growing understanding of how such 

 changes adversely affect diversity. (Key con- 

 cepts that have aided this understanding are 

 described in box 3-A.) 



DIVERSITY LOSS 



The problem of diversity loss is broader than 

 extinction of species because diversity occurs 

 at each level of biological organization. 



Ecosystem diversity: A landscape inter- 

 spersed with agricultural fields, grasslands, 

 and woodlands has more diversity than the 



